The invention relates to a tensioning device of a traction mechanism drive, with a tensioning piston, which is mounted so that it can move in the axial direction and which is provided with an attachment shaft facing the traction mechanism, with a tensioning shoe made from plastic mounted via a support hole on the attachment shaft, and with a disk-shaped metallic support element having a support hole fixed to the attachment shaft.
Traction mechanism drives, such as chain drives and toothed belt drives, are used in many machines for power transfer due to their reliability and cost-effectiveness, e.g., also for driving camshafts in reciprocating internal combustion engines of motor vehicles. Traction mechanism drives frequently have vibration dampers in the form of housing-fixed sliding shoes, which are preferably made from a low-friction polymer plastic or from a guide rail made from metal coated with this material and which are in sliding contact with the traction mechanism, for preventing vibrations of the traction mechanism chain or toothed belt.
The sliding shoes could be arranged both on the tensioned side and also on the loose side of the traction mechanism. For increasing the angle of belt wrap on the driving and driven gears, but especially for compensating for longitudinal expansion of the traction mechanism occurring during operation, traction mechanism drives usually also have a tensioning device arranged on the loose side. This tensioning device has available a tensioning piston, which is mounted so that it can move in the axial direction and which acts on a tensioning shoe loaded by a spring element and/or a compression means. This tensioning shoe deflects the loose side of the traction mechanism normal toward its direction of motion and also toward the rotational axes of the gears and thus compensates for the longitudinal expansion and tensions the traction mechanism.
From DE 40 13 190 C2, a tensioning device for a chain drive is known, in which a tensioning shoe is formed as a separate component and which is mounted so that it can rotate about a housing-fixed shaft. A tensioning piston, which loads the tensioning shoe with a compressive force, is located at a distance from the shaft and thus presses this shoe against the loose side of the chain, whereby this is tensioned. Due to the slide-shifting contact of the tensioning shoe with the tensioning piston, rotation due to operation is largely prevented between the tensioning piston and the tensioning shoe. A disadvantage in this known tensioning device, however, is the large number of components and the relatively large spatial requirements.
In DE 195 36 643 A1, a tensioning device for a chain drive is described, in which two tensioning shoes made from a polymer plastic and aligned opposite one another are fixed rigidly to a tensioning lever, which is formed as a rocking lever and which is mounted between the two tensioning shoes so that it can rotate about a housing-fixed shaft. A tensioning piston loads the tensioning lever at a distance from the shaft with a compressive force and thus presses both tensioning shoes in opposite directions against the loose side of the chain, whereby this is tensioned. Due to the rotating support of the tensioning lever and the sliding contact of the tensioning lever with the tensioning piston, no large rotation occurs between the tensioning shoes and the tensioning lever. The number of components and the spatial requirements, however, are increased disadvantageously relative to the construction named above.
For use especially under narrow spatial relationships, compact tensioning devices have been developed, in which the tensioning shoe is connected essentially rigidly to the tensioning piston.
A first tensioning device constructed in this way is known as a component of a camshaft chain drive from DE 40 06 910 C1, in which a tensioning shoe is arranged, with less projection of the tensioning piston and thus unfavorably smaller contact surface to the chain, directly on the attachment shaft of the tensioning piston.
Another such tensioning device is described in DE 698 16 264 T2, in particular, for use in a chain drive of a camshaft drive, in which the tensioning shoe has a clear projection relative to the tensioning piston and is shifted laterally onto a disk-shaped support element fixed rigidly on the tensioning piston on the outside and is also secured with a screw connection. In this construction, the high expense for the production and the assembly of the individual parts is disadvantageous.
In addition, a tensioning device that can be produced simply and economically is known, in which a tensioning shoe with large projection of the tensioning piston is produced from a polymer plastic, provided with a central support hole, and connected to this rigidly by insertion on a cylindrical support shaft of the tensioning piston. In this construction, however, especially due to the large projection, usually fluctuating bending loads occurring in operation between the tensioning shoe and the tensioning piston can lead to tensioning excesses in the area of the support hole of the tensioning shoe, which can lead to overloading and possibly even to the destruction of the tensioning shoe.
For better load distribution and transfer of bending forces from the tensioning shoe into the tensioning piston, a disk-shaped metallic transfer element with a central support hole in front of the tensioning shoe is pressed onto the support shaft and fused or welded with this. In this way, the force transfer between the tensioning shoe and the tensioning piston is definitely improved, but disadvantageously the production process becomes more complicated. In addition, the fusing or welding of the support element with the tensioning piston can lead to undesired deformation and twisting in both components.